1. Field of Invention
The present invention relates generally to medical devices and methods of use for the treatment and/or management of cardiovascular, neurological, and renal disorders, and more specifically to devices and methods for controlling the energy consumption of a battery in an implantable pulse generator of baroreflex systems for the treatment and/or management of cardiovascular, neurological, and renal disorders and their underlying causes and conditions.
Implantable pulse generator medical devices are well known in the art, and include medical devices. Generally, these medical devices comprise an implantable pulse generator unit including a battery as the source of energy. A problem associated with pulse generators (e.g., implantable or external) is battery depletion. Such problems include: loss of therapy, which in some cases may be life-sustaining; rebound or similar disadvantageous effects if the therapy were abruptly discontinued (as for example in the case of pulse generators for use in regulating blood pressure, abrupt cessation of therapy may result in the blood pressure to revert to levels higher than even that of pre-therapy baseline. Hence, such abrupt cessation needs to be avoided, thus there is the advantage of avoiding loss of battery, or at least reducing therapy gradually before battery depletion). Furthermore, another problem is the loss of data stored in volatile memory in the device. Thus, it would be important to avoid abrupt cessation of therapy due to loss of battery, or at least reducing the therapy gradually before the depletion of the battery. Furthermore, such abrupt cessation may also result in loss of data stored in the volatile memory in the device.
Hypertension, or high blood pressure, is a major cardiovascular disorder that is estimated to affect 65 million people in the United States alone, and is a leading cause of heart failure and stroke. It is listed as a primary or contributing cause of death in over 200,000 patients per year in the United States alone. Hypertension occurs in part when the body's smaller blood vessels (arterioles) constrict, causing an increase in blood pressure. Because the blood vessels constrict, the heart must work harder to maintain blood flow at the higher pressures. Sustained hypertension may eventually result in damage to multiple body organs, including the kidneys, brain, eyes and other tissues, causing a variety of maladies associated therewith. The elevated blood pressure may also damage the lining of the blood vessels, accelerating the process of atherosclerosis and increasing the likelihood that a blood clot may develop. This could lead to a heart attack and/or stroke.
Sustained high blood pressure may eventually result in an enlarged and damaged heart (hypertrophy), which may lead to heart failure. Heart failure is the final common expression of a variety of cardiovascular disorders, including ischemic heart disease. It is characterized by an inability of the heart to pump enough blood to meet the body's needs and results in fatigue, reduced exercise capacity and poor survival. It is estimated that approximately 5,000,000 people in the United States suffer from heart failure, directly leading to 39,000 deaths per year and contributing to another 225,000 deaths per year.
A number of drug treatments have been proposed for the management of hypertension, heart failure, and other cardiovascular disorders. These include vasodilators to reduce the blood pressure and ease the workload of the heart, diuretics to reduce fluid overload, inhibitors and blocking agents of the body's neurohormonal responses, and other medicaments. Various surgical procedures have also been proposed for these maladies. For example, heart transplantation has been proposed for patients who suffer from severe, refractory heart failure. Alternatively, an implantable medical device such as a ventricular assist device (VAD) may be implanted in the chest to increase the pumping action of the heart. Alternatively, an intra-aortic balloon pump (IABP) may be used for maintaining heart function for short periods of time, but typically no longer than one month.
Although each of these approaches is beneficial in some ways, each of the therapies has its own disadvantages. For example, drug therapy is often incompletely effective. Drugs often have unwanted side effects and may need to be given in complex regimens. These and other factors contribute to poor patient compliance with medical therapy. Drug therapy may also be expensive, adding to the health care costs associated with these disorders.
2. Brief Description of the Background Art
It has been known for decades that the wall of the carotid sinus, a structure at the bifurcation of the common carotid arteries, contains stretch receptors (baroreceptors) that are sensitive to the blood pressure. These receptors send signals via the carotid sinus nerve to the brain, which in turn regulates the cardiovascular system to maintain normal blood pressure (the baroreflex), in part through modulation of the sympathetic and/or parasympathetic, collectively the autonomic, nervous system. Electrical stimulation of the carotid sinus nerve (baropacing) has previously been proposed to reduce blood pressure and the workload of the heart in the treatment of high blood pressure and angina.
Rau et al. (2001) Biological Psychology 57:179-201 describes animal and human experiments involving baroreceptor stimulation. U.S. Pat. Nos. 6,073,048 and 6,178,349, each having a common inventor with the present application, describe the stimulation of nerves to regulate the heart, vasculature, and other body systems. U.S. Pat. No. 6,522,926, assigned to the assignee of the present application, describes a number of systems and methods intended to activate baroreceptors in the carotid sinus and elsewhere in order to induce the baroreflex system. Numerous specific approaches are described, including the use of coil electrodes placed over the exterior of the carotid sinus near the carotid bifurcation. Nerve stimulation for other purposes is described in, for example, U.S. Pat. Nos. 6,292,695 B1 and 5,700,282. Publications which describe the existence of baroreceptors and/or related receptors in the venous vasculature and atria include Goldberger et al. (1999) J. Neuro. Meth. 91:109-114; Kostreva and Pontus (1993)Am. J. Physiol. 265:G15-G20; Coleridge et al. (1973) Circ. Res. 23:87-97; Mifflin and Kunze (1982) Circ. Res. 51:241-249; and Schaurte et al. (2000) J. Cardiovasc Electrophysiol. 11:64-69. U.S. Pat. No. 5,203,326 describes an anti-arrhythmia pacemaker. PCT patent application publication number WO 99/51286 describes a system for regulating blood flow to a portion of the vasculature to treat heart disease. The full texts and disclosures of all the references listed above (including the “related applications” earlier referenced above) are fully incorporated herein by reference in their entirety.
Cardiac resynchronization therapy (CRT) devices are known. Examples of CRT devices and methods are described in U.S. Pat. Nos. 6,768,923; 6,766,189; 6,748,272; 6,704,598; 6,701,186; and 6,666,826; the full disclosures of which are hereby incorporated by reference in their entirety.
An example of an implantable blood pressure measurement device that may be disposed about a blood vessel is disclosed in U.S. Pat. No. 6,106,477 to Miesel et al. An example of a subcutaneous ECG monitor is available from Medtronic under the trade name REVEAL ILR and is disclosed in PCT Publication No. WO 98/02209. Other examples are disclosed in U.S. Pat. Nos. 5,987,352 and 5,331,966. Examples of devices and methods for measuring absolute blood pressure utilizing an ambient pressure reference are disclosed in U.S. Pat. No. 5,810,735 to Halperin et al.; U.S. Pat. No. 5,904,708 to Goedeke; and PCT Publication No. WO 00/16686 to Brockway et al. The full texts and disclosures of all the references listed above are hereby incorporated fully by reference in their entirety.